Nucleated propylene-based polyolefin compositions

Abstract

A polyolefin composition, particularly fit for the production of extrusion blow molded articles, comprising (a) a propylene-ethylene copolymer having a content of units deriving from ethylene of 4.0% by weight or higher, and (b) a nucleating agent and having a crystallization temperature (Tc) higher than 117° C. can be obtained by copolymerizing propylene and ethylene in the presence of a catalyst system obtained by contacting a solid catalyst component comprising a magnesium halide, a titanium compound having at least a Ti-halogen bond and at least two electron donor compounds one of which being present in an amount from 40 to 90% by mol with respect to the total amount of donors and selected from succinates and the other selected from 1,3 diethers, an aluminum hydrocarbyl compound, and optionally an external electron donor compound.

1 . A polyolefin composition comprising:
 (i) a propylene-ethylene copolymer having a content of units deriving from ethylene of about 4.0% by weight or higher, and   (ii) a nucleating agent;   wherein the composition has a crystallization temperature (Tc), measured by DSC, higher than 117° C.   
     
     
         2 . The polyolefin composition according to  claim 1 , wherein the nucleating agent is present in the composition in amounts of up to about 2500 ppm. 
     
     
         3 . The polyolefin composition according to  claim 1 , wherein the nucleating agent is selected among 3,4-dimethyldibenzylidenesorbitol, aluminum-hydroxy-bis[2,2′-methylene-bis(4,6-di-t-butylphenyl)phosphate], sodium or lithium 2,2′-methylene-bis(4,6-ditertbutylphenyl)phosphate and bicyclo[2.2.1]heptane-2,3-dicarboxylic acid, disodium salt (1R,2R,3R,4S). 
     
     
         4 . A process for the preparation of a propylene-ethylene copolymer comprising the step of copolymerizing propylene and ethylene in the presence of a catalyst system comprising the product obtained by contacting the following components:
 (a) a solid catalyst component comprising a magnesium halide, a titanium compound having at least a Ti-halogen bond and at least two electron donor compounds one of which being present in an amount from 40 to 90% by mol with respect to the total amount of donors and selected from succinates and the other being selected from 1,3 diethers,   (b) an aluminum hydrocarbyl compound, and   (c) optionally an external electron donor compound.   
     
     
         5 . The process according to  claim 4 , wherein the succinate is of formula (I): 
       
         
           
           
               
               
           
         
         wherein the radicals R 1  and R 2 , equal to, or different from, each other are a C 1 -C 20  linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; and the radicals R 3  and R 4  equal to, or different from, each other, are C 1 -C 20  alkyl, C 3 -C 20  cycloalkyl, C 5 -C 20  aryl, arylalkyl or alkylaryl group with the proviso that at least one of them is a branched alkyl; said compounds being, with respect to the two asymmetric carbon atoms identified in the structure of formula (I), stereoisomers of the type (S,R) or (R,S). 
       
     
     
         6 . The process according to  claim 4 , wherein the 1,3-diether is of formula (II): 
       
         
           
           
               
               
           
         
         wherein R I  and R II  are the same or different and are hydrogen or linear or branched C 1 -C 18  hydrocarbon groups which can also form one or more cyclic structures; R III  groups, equal or different from each other, are hydrogen or C 1 -C 18  hydrocarbon groups; R IV  groups equal or different from each other, have the same meaning of R II  except that they cannot be hydrogen; each of R I  to R IV  groups can contain heteroatoms selected from halogens, N, O, S and Si. 
       
     
     
         7 . The process according to  claim 4 , wherein the catalyst component (a) has an average particle size ranging from about 15 to about 80 μm. 
     
     
         8 . The process according to  claim 4 , wherein the succinate is present in amount ranging from about 40 to about 90% by mol with respect to the total amount of internal donors. 
     
     
         9 . (canceled) 
     
     
         10 . A process for producing extrusion blow molded articles comprising the use of a polyolefin composition comprising the steps of:
 (i) extruding a parison, from a molten polyolefin composition comprising:
 (a) a propylene-ethylene copolymer having a content of units deriving from ethylene of 4.0% by weight or higher, and 
 (b) a nucleating agent, 
 wherein the composition has a crystallization temperature (Tc), measured by DSC; and 
 (c) blow molding the extruded parison to form a blow-molded article. 
   
     
     
         11 . The polyolefin composition of  claim 1  formed into a blow-molded article. 
     
     
         12 . The polyolefin composition of  claim 1 , wherein the propylene-ethylene copolymer has a content of units deriving from ethylene ranging from about 4.0% by weight to about 7.0% by weight. 
     
     
         13 . The polyolefin composition of  claim 1 , wherein the crystallization temperature (Tc), measured by DSC, higher than 117.5° C. 
     
     
         14 . The polyolefin composition of  claim 13 , wherein the crystallization temperature (Tc), measured by DSC, higher than 118° C. 
     
     
         15 . The polyolefin composition of  claim 2 , wherein the nucleating agent is present in the composition in amounts ranging from about 500 ppm to about 2000 ppm. 
     
     
         16 . The polyolefin composition of  claim 10 , wherein the propylene-ethylene copolymer has a content of units deriving from ethylene ranging from about 4.0% by weight to about 7.0% by weight. 
     
     
         17 . The polyolefin composition of  claim 10 , wherein the crystallization temperature (Tc), measured by DSC, higher than 117.5° C. 
     
     
         18 . The polyolefin composition of  claim 17 , wherein the crystallization temperature (Tc), measured by DSC, higher than 118° C. 
     
     
         19 . The polyolefin composition of  claim 10 , wherein the nucleating agent is present in the composition in amounts up to about 2500 ppm. 
     
     
         20 . The polyolefin composition of  claim 19 , wherein the nucleating agent is present in the composition in amounts ranging from about 500 ppm to about 2000 ppm.